1. Field of the Invention
The present invention relates generally to an image forming method in an image forming apparatus utilizing an electrophotographic system such as a copying machine, a printer, or a facsimile, and more particularly, to an image forming method in which a toner image formed on the surface of an image carrier is transferred to a recording medium, after which residues such as toner particles remaining on the surface of the image carrier can be stably cleaned by a cleaning blade composed of an elastic member.
2. Description of the Prior Art
Generally in forming images in an image forming apparatus utilizing an electrophotographic system such as a copying machine, a printer, or a facsimile, an image carrier 1 in a cylindrical shape is rotated, to charge the surface of the image carrier 1 by a charger 2, after which an electrostatic latent image is formed on the image carrier 1 by suitable exposing means (not shown), toner particles 4 in a developing agent are supplied to the electrostatic latent image on the image carrier 1 from a developing device 3, to form a toner image on the surface of the image carrier 1, the toner image is transferred to a recording medium 6 such as paper by a transferring and separating charger 5, and the recording medium 6 is separated from the image carrier 1, as shown in FIG. 1.
The recording medium 6 is introduced into a fixing roller 7, and the toner image transferred in the above-mentioned manner is fixed to the recording medium 6 by the fixing roller 7, while residues such as the toner particles 4 remaining on the surface of the image carrier 1 after the transfer are removed from the surface of the image carrier 1 by a cleaning device 8, after which a potential remaining on the image carrier 1 is discharged by a discharger (not shown).
As the cleaning device 8 for removing the residues such as the toner particles 4 remaining on the surface of the image carrier 1 after the transfer in the above-mentioned manner, various devices such as a device using a cleaning brush are employed. A device so adapted that a cleaning blade 8a composed of an elastic member is used, an end of the cleaning blade 8a is caused to abut against the surface of the image carrier 1, and the residues such as the toner particles 4 remaining on the surface of the image carrier 1 are removed by the cleaning blade 8a, as shown in FIG. 1, is frequently employed in that it is low in cost and is simple in construction.
On the other hand, in recent years, toner particles having small particle diameters have been used as the toner particles 4 in order to reproduce precise images in the above-mentioned image forming apparatus.
If the toner particles 4 having small particle diameters are used, however, in removing the residues such as the toner particles 4 remaining on the surface of the image carrier 1 from the surface of the image carrier 1 by the cleaning blade 8a, the toner particles 4 slip between the image carrier 1 and the cleaning blade 8a. Therefore, the toner particles 4 are liable to be insufficiently removed from the surface of the image carrier 1, whereby noise is produced in formed images.
Specifically, in a case where the toner particles 4 having small particle diameters are produced by the kneading and pulverizing method conventionally commonly used, even if the toner particles 4 having small particle diameters are classified by an air classifier or the like, fine powder included in the toner particles 4 is not sufficiently removed. When the fine powder, together with the toner particles 4, is supplied to the surface of the image carrier 1, therefore, the fine powder is not removed from the surface of the image carrier 1 by the cleaning blade 8a, to pass between the cleaning blade 8a and the image carrier 1. At the time of the passage, the fine powder adheres to the surface of the image carrier 1, whereby noise is produced in formed images.
On the other hand, in a case where the toner particles 4 having small particle diameters are produced by the wet granulating method such as the suspension polymerization method or the emulsion dispersion method, the particle diameters of the toner particles 4 thus obtained are distributed in a narrow range and are relatively uniform. The shapes of the toner particles 4 are approximately spherical. When the end of the cleaning blade 8a is pressed against the surface of the image carrier 1, to remove the residues such as the toner particles 4 remaining on the surface of the image carrier 1 as mentioned above, the toner particles 4 whose shapes are approximately spherical slip between the image carrier 1 and the cleaning blade 8a. Therefore, the toner particles 4 are not sufficiently removed from the surface of the image carrier 1, whereby noise is produced in formed images.
Furthermore, in a case where the toner particles 4 having small particle diameters are agitated with magnetic carriers, to frictionally charge the toner particles 4, the rising of the charging of the toner particles 4 is degraded if the magnetic carriers are conventionally commonly used. Therefore, magnetic carriers having small particle diameters have been used as the magnetic carriers.
When the magnetic carriers having small particle diameters are used, however, the carriers are liable to adhere to the image carrier 1. If the magnetic carriers adhering on the surface of the image carrier 1 are not sufficiently removed by the cleaning blade 8a, the surface of the image carrier 1 is damaged by the carriers, and the carriers are embedded in the surface of the image carrier 1, whereby noise is produced in formed images.
When binder-type carriers including magnetic powder in binder resin are used as the above-mentioned magnetic careers, the binder-type carriers are generally produced by the kneading and pulverizing method. At the time of the pulverization, therefore, the magnetic powder is liberated, and the magnetic powder thus liberated is included in the carriers. The liberated magnetic powder adheres to the surface of the image carrier 1, and is embedded in the surface of the image carrier 1 without being sufficiently removed by the cleaning blade 8a, whereby noise is produced in formed images.
In recent years, in order to miniaturize the above-mentioned image forming apparatus and increase the speed thereof, an image carrier having a small diameter has been used as the above-mentioned image carrier 1, and the image carrier 1 is rotated at high speed, to form images.
When the cleaning blade 8a is pressed against the surface of the image carrier 1 having a small diameter which is thus rotated at high speed, to remove the residues such as the toner particles 4 remaining on the surface of the image carrier 1, the cleaning capability is further degraded, whereby the toner particles 4 are often insufficiently removed from the surface of the image carrier 1. Consequently, much noise or the like is produced in formed images, so that good images are not obtained.
Furthermore, in recent years, in transferring the toner image to the recording medium 6 and then fixing the toner image on the recording medium 6 by the fixing roller 7, a small-sized fixing roller has been used as the fixing roller 7, and temperatures at the time of fixing in the fixing roller 7 have been lowered in order to miniaturize the image forming apparatus and achieve energy saving as well as shorten warm-up time.
When the toner particles 4 transferred to the recording medium 6 are thus fixed to the small-sized fixing roller 7 at low temperatures, the nip width in the fixing roller 7 is small, and the fixing is performed at low temperatures, whereby superior fixing properties at low temperatures are required for the toner particles 4. At the beginning of heating of the fixing roller 7, the fixing roller 7 may, in some cases, be temporarily heated to high temperatures of 200.degree. C. or more. Therefore, superior offset resistance to high temperatures is also required for the toner particles 4, and offset resistance in a low-temperature region and a high-temperature region is required.
In the toner particles 4 fixed at low temperatures as mentioned above, therefore, an anti-offset material for preventing offset in the low-temperature region and an anti-offset material for preventing offset in the high temperature region are contained.
Each of the anti-offset materials included in the toner particles 4 does not generally have compatibility with the binder resin used for the toner particles 4, and exists in a state where it is dispersed in a particle shape in the binder resin.
When the toner particles 4 containing each of the anti-offset materials are produced, therefore, the anti-offset material may, in some cases, exist as liberated fine powder in the toner particles 4. For example, when the toner particles 4 are produced by the kneading and pulverizing method conventionally commonly used, each of the anti-offset materials exists as liberated fine powder in the toner particles 4. When the toner particles 4 having small particle diameters are used in order to form precise images as mentioned above, the fine powder of the anti-offset material cannot be sufficiently removed by classification, for example, whereby much fine powder of the anti-offset material exists in the toner particles 4.
In a case where development is performed using the toner particles 4 in which the fine powder of the anti-offset material exists, when the fine powder of the anti-offset material, together with the toner particles 4, is supplied to the image carrier 1, the fine powder of the anti-offset material is not sufficiently removed from the surface of the image carrier 1 by the cleaning blade 8a to pass through the cleaning blade 8a. At the time of the passage, the fine powder of the anti-offset material is film-formed on the surface of the image carrier 1, whereby the chargeability of the image carrier 1 in this portion is degraded. Consequently, noise is produced in formed images.